The genetic control of the synthesis and function of macromolecular cell structures is studied by two approaches: 1. Mutations in structural and regulatory genes controlling chlorophyll synthesis in barely are used to analyze the role of the membrane protein protochlorophyll holochrome in the regulation of porphyrin synthesis and in the assembly of the photosynthetic membrane. Studies on organelle biogenesis with the aid of gene mutants concern the synthesis and function of membrane proteins and lipids. 2. Precise pairing of homologous chromosomes in meiosis is a prerequisite for crossing-over, and is accomplished by the ribonucleoproteins of the synaptinemal complex. The assembly of the synaptinemal complex and its function in chromosome recognition is studied in certain Drosophila and Bombyx genotypes as well as in Lilium and Neottiella. Isolation and chemical characterization of the synaptinemal complex from yeast and Allomyces are attempted. Such isolation is a prerequiite for studying the questions, whether certain components of the synaptinemal complex are products of specific recognition genes and others serve functions in the molecular events of crossing-over.